Medical technology has long since endeavored to correct valvular defects such as, for example, aortic valve insufficiencies or aortic valve stenosis, by means of non-surgical, transarterial access; i.e. without requiring open heart surgery, with implantation by way of catheter. In the process, various different stent systems with various different advantages and disadvantages have been proposed, some which can also be inserted transarterially into the body of a patient via a catheter delivery system.
The terms “aortic valve stenosis and/or aortic valve insufficiency” as used herein generally refer to a congenital or acquired dysfunction of one or more cardiac valves. Such valvular disorders can affect any of the four cardiac valves, whereby the valves in the left ventricle or left chamber (aortic and mitral valve) are typically more affected than those on the right side of the heart (pulmonary and tricuspid valve). The dysfunction can be a constriction (stenosis), an incompetence (insufficiency) or a combination of the two (combined vitium).
Minimally invasive forms of treatment have recently been developed which are in particular characterized by allowing the procedure to be performed under local anesthesia. One approach provides for using a catheter system to implant an expandable stent, to which a collapsible prosthetic heart valve has been affixed, into a human body. Such an expandable prosthetic heart valve can be guided via a delivery or catheter system to the implantation site within the heart through an inguinal artery or vein. After reaching the implantation site, the stent can then be unfolded. After unfolding, the prosthetic heart valve can be anchored in the respective blood vessel at least in an area close to the heart, for example with the aid of anchoring hooks. The actual prosthetic heart valve is usually positioned in the proximal area of the stent.
For example, the WO 2004/019825 A1 printed publication describes a heart valve stent for a heart valve prosthesis. This stent can be introduced into the site of implantation in the patient's heart via a medical delivery system to treat an aortic valve stenosis and/or aortic valve insufficiency in a minimally invasive manner.
Known conventional systems for implanting a prosthetic heart valve introduce an expandable stent system transarterially/transfemorally or transapically into the body of the patient using a medical delivery system. This type of stent system consists for example of an expandable anchoring support (hereinafter also referred to as “cardiac valve stent” or simply “stent”), to which the actual prosthetic heart valve is affixed or can be affixed, preferably at the end region nearest the heart (proximal end).
The explanations disclosed herein with respect to a “stent system” are also applicable to a “stent”.
The term “medical delivery system” as used herein generally refers to a medical system with which a stent system can be advanced in minimally invasive fashion to the site of implantation in the patient's heart, for example to treat an aortic valve stenosis and/or aortic valve insufficiency. In the present context, “minimally invasive” means a heart-lung machine is not needed when performing the procedure on the anaesthetized patient such that not only can the medical procedure be performed at reasonable cost, but there is also less physical and psychological strain on the patient.
A medical delivery system usually comprises a catheter system by means of which a stent, as needed with a prosthetic heart valve affixed thereto in folded state, can be introduced into the patient's body in its folded state. For example, the medical delivery system can exhibit a catheter tip having at least one manipulatable receiving area at a proximal end section of the catheter system; i.e. closest to the heart. It is moreover conceivable for the medical delivery system to exhibit a handle at the distal end section of the catheter system; i.e. at the end section of the catheter system farthest from the heart and the catheter tip, with which the at least one receiving area of the caterer tip can be appropriately manipulated such that the expandable stent accommodated in the catheter tip, as needed with a prosthetic heart valve affixed thereto, can be incrementally released from the catheter tip according to a predefined or predefinable sequence of events.
In this disclosure, the expression “catheter system” means a system that can be inserted into a body cavity, duct or vessel. A catheter system thereby allows access by surgical instruments. The process of inserting a catheter system is catheterisation. In most uses a catheter system is a thin, flexible tube: a “soft” catheter system; in some uses, it is a larger, solid tube: a “hard” catheter system.
To introduce the stent system, the stent together with the prosthetic heart valve affixed as needed thereto, is loaded into the tip of the medical delivery system's catheter. In order to do so, the stent, as needed with the prosthetic heart valve affixed thereto, needs to exhibit a first predefinable shape in which the stent or the stent and the prosthetic heart valve affixed thereto is/are in a compressed or folded state. In its first predefined state, the stent, as needed with the prosthetic heart valve affixed thereto, exhibits a diameter which is essentially determined by the diameter of the catheter tip of the medical delivery system.
For the majority of patients undergoing treatment, it is preferable for the stent, as needed with the prosthetic heart valve affixed thereto, to have an outer diameter of approximately 7.0 mm to approximately 5.0 mm in its first shape so that the stent system can be introduced with a 21F delivery system (given an external diameter of 7.0 mm) or with a 15F delivery system (given an external diameter of 5.0 mm).
After the stent system has been released from the catheter tip, in the implanted state respectively, the stent system exhibits a second predefined shape in which the stent or the stent and the prosthetic heart valve affixed thereto is/are in an expanded state. Depending on the patient being treated, it is preferable for the stent to exhibit a diameter of between 19.0 mm and 27.0 mm in its second shape and implanted state.
Thus, the first shape transitions to the second shape by a cross-sectional widening, wherein the stent stretches radially and presses against the vascular wall of a blood vessel near the heart and thus fixes a prosthetic heart valve affixed as needed to the stent at the site of implantation. The cross-sectional widening can be effected by a balloon system when the stent is implanted with the help of a so called balloon catheter system.
On the other hand, it is also known from medical technology to construct the stent from a superelastic shape memory material which is designed such that the stent can transform from a temporary shape into a permanent shape under the influence of an external stimulus. The temporary shape thereby corresponds to the stent's first shape when the stent, as needed with the prosthetic heart valve affixed thereto, is in its folded state. The permanent shape corresponds to the stent's second shape when in its expanded state. An example of a suitable shape memory material would be nitinol, e.g., an equiatomic alloy of nickel and titanium.
Turning out to be disadvantageous with conventional systems for implanting a prosthetic heart valve as known to date, however, has been that not only the actual implantation of the stent, as needed with the prosthetic heart valve affixed thereto, but also the preparation needed for the implant procedure is relatively complicated, difficult and laborious. Apart from the complicated implanting of the stent, as needed with a prosthetic heart valve affixed thereto, to replace an insufficient native heart valve, for example, there is also the fundamental problem of the stent and/or the stent and a prosthetic heart valve affixed thereto being damaged when the stent, as needed with a prosthetic heart valve affixed thereto, is loaded into the tip of the catheter of the medical delivery system in preparation for the surgery. In particular with self-expanding stent systems, the stent, as needed with a prosthetic heart valve affixed thereto, has to be compressed so that it will then be in its first shape and be able to be introduced into the tip of the catheter of a medical delivery system. This subjects the stent to considerable compressive forces in order to overcome the self-expanding stent structure's expansion forces and achieve the desired reduction in cross-section.
Similar circumstances however also apply to stent systems which are implanted using balloon catheter systems.
In conjunction hereto, often likewise regarded as problematic is that when preparing for the implant procedure, the stent, as needed with a prosthetic heart valve affixed thereto, can often only be loaded into the tip of the catheter of a medical delivery system by an experienced perfusionist or by product specialists so as to avoid damaging the stent system and so that the stent system can be properly transformed into its defined first shape.
Without special compressing mechanisms or loading systems, the known systems are thus coupled with the fundamental risk of damage to the stent system or it not properly being transformed into its defined first shape, for example due to an oversight on the part of the perfusionist or product specialist or some other incident occurring during the compressing of the stent system. Damage which occurs when compressing the stent system or when loading the compressed stent system into the catheter tip of the medical delivery system are often not noted until the actual implant procedure is underway, for example when the positioning and/or fixing of the prosthetic heart valve at the site of implantation at the heart by means of the stent is imprecise, when the stent will not properly expand at the implantation site in the heart, or when it is for example determined that the implanted prosthetic heart valve cannot or not adequately enough assume the function of the native heart valve to be replaced.